1. Field of the Invention
The present invention relates to a portable electronic apparatus, such as a computer or a word processor and, in particular, a structure for incorporating an optional component unit, such as a MODEM for use in a telephone line, into a base unit of the apparatus.
2. Description of the Related Art
Recently, various book- and laptop-type portable computers have been proposed which incorporate a keyboard and a flat panel-type display unit into a flat box-like base unit.
These apparatuses enable an optional component unit, such as a MODEM connected to a telephone line, to be added, if required. In the conventional portable computer, a storage space for incorporating an optional component unit as an expanded unit therein is initially secured in the base unit. The storage space has an opening provided in the peripheral surface of the base unit and walls defining the opening and inside of the base unit. The optional component unit in the storage space has a case for closing the opening. The case constitutes a portion of the peripheral surface of the base unit in a continuous relation. A printed circuit board is supported in the case and has a circuit pattern printed as a printed pattern and various circuit parts electrically connected to the circuit pattern. When the opening of the storage space is closed by the case, the printed circuit board and circuit parts are held in a space defined by the case and defined walls of the storage space.
Some of the optional components produce high frequency noise during operation, sometimes causing radio interference and communication disturbance. In order to achieve an electromagnetic shield to reduce radio interference and communication disturbance in the conventional portable computer, the case and defined walls which surround the optional component unit are covered with a conductive layer, such as a plating layer.
Recently a printed circuit board constituting the optional component unit has been fabricated by other manufactures, such as the third party. However, the fabricated printed circuit board is not stable in its quality and sometimes the circuit pattern deviates out of standards. If the printed circuit board having an out-of-standard circuit pattern is supported in the case, the circuit pattern and conductive layer may be short-circuited at an area of contact of the printed circuit board with the case due to the conductive covering of the case. That is, since the conductive layer covers projections and hooks on the case so as to support the printed circuit board thereon, it is substantially impossible to completely cover the conductive sheet, and so on, with a nonconductive layer. Since the conductive layer may naturally be exposed at an area supporting the printed circuit board, the optional component unit may fail to operate, or may be damaged, due to short-circuiting between the conductive layer and the circuit pattern.